Demodulator for an isolation communication channel for dual communication

ABSTRACT

An integrated circuit includes a demodulator to demodulate a signal simultaneously transmitted over an isolation communication channel and obtain gate information and configuration information. The demodulator includes a gate demodulation path and a configuration demodulation path. The received signal oscillates at a first frequency to represent a first state, oscillates at different frequencies to represent a seconds state, oscillates at a third frequency (or third and fourth frequencies), which are lower than the first frequency, to represent a third state, and the received signal is steady state to represent a fourth state. The gate demodulation path detects the first and second states. The configuration demodulation path includes first and second sub-demodulation paths. An envelope detector in the first sub-demodulation path detects the second state and the second sub-demodulation path detects the third state. The configuration demodulation paths uses an output of the gate demodulation path.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application relates to the application entitled “Transmitter ForDual Communication Over An Isolation Channel”, naming Carlos JesusBriseno-Vidrios et al. as inventors, application Ser. No. 17/066,244,filed Oct. 8, 2020, and this application relates to the patentapplication entitled “Interface For Passing Control Information Over AnIsolation Channel” naming Michael R. May et al. as inventors,application Ser. No. 17/066,251, filed Oct. 8, 2020, all of whichapplications were filed on the same day as the present application andall of which applications are incorporated herein by reference.

BACKGROUND Field of the Invention

The invention relates to isolation technology and more particularly tocommunication across an isolation barrier.

Description of the Related Art

Isolation communication channels are utilized in various applicationswhere necessary to prevent current flow between isolated electriccircuits by using an isolation barrier while still maintainingcommunication between the circuits. The isolation may be required forsignal isolation, safety, or for other reasons. Communication betweenisolated circuits has typically involved a transmitter and receivercommunicating over an isolation communication channel to provide, e.g.,control information between the different voltage domains. The isolationcommunication channel may be implemented, e.g., using capacitive,inductive (transformers), or optical (opto-isolators) isolationtechniques. In a typical isolation application, a control systemprovides one or more control signals for controlling a load system.During normal operation, a large DC or transient voltage difference mayexist between the domain of the control system and the domain of theload system, thus requiring an isolation barrier between the controlsystem and the load system. Isolation of the circuits in the separatevoltage domains using an isolation barrier prevents damaging currentsfrom flowing between the control system and the load system by a directconduction path, while the isolation communication channel allowscommunication between the two systems.

FIG. 1 illustrates a prior art system 100 that includes an isolated gatedriver 101. The gate driver 101 receives control information for drivinga gate signal of a high-power transistor 102 that is electricallyisolated from the control functionality providing the controlinformation. In the exemplary system 100, controller 103, which may be amicroprocessor, microcontroller, or other suitable processing device,operates in a first domain (i.e., a domain including VDD1 and VDD2). Thecontroller 103 provides a gate signal to control a load system operatingin a second domain i.e., a domain including VDD3 and VDD4. The isolationbarrier electrically isolates the primary side including VDD1 (e.g.,less than twenty volts) and VDD2 (e.g., less than twenty volts) anddevices coupled thereto, from the secondary side including VDD3 (e.g.,tens of volts) and VDD4 (e.g., hundreds of volts) and devices coupledthereto.

The isolated gate driver 101 includes a transmitter circuit 106 and areceiver circuit 108, which communicate over an isolation communicationchannel 109. In the system 100, controller 103 supplies gate information(GATE) to the transmitter circuit 106 in the first voltage domain. Thetransmitter circuit 106 transmits the gate information to the receivercircuit 108 in the second voltage domain. The receiver circuit 108 usesthe gate information to generate a gate drive signal 120 to drive thehigh-power transistor 102 that is used to control a system load.

While the isolated gate driver allows communication across the isolationbarrier, improvements in such communication is desirable to provide moreprecise control over the system load.

SUMMARY OF EMBODIMENTS OF THE INVENTION

Accordingly, in one embodiment a method includes receiving a signaltransmitted across a single isolation communication channel as areceived signal. The method further includes demodulating the receivedsignal to determine respective values for gate information andconfiguration information contained in the received signal based onwhich of four states the received signal represents.

In another embodiment, an apparatus includes one or more input terminalsto receive a signal transmitted across an isolation communicationchannel. A demodulator circuit is coupled to the one or more inputterminals to demodulate a received signal to obtain gate information andto obtain configuration information. Respective values of the gateinformation and the configuration information are determined accordingto which one of four states the demodulator circuit detects in thereceived signal.

In another embodiment an integrated circuit includes aa demodulator todemodulate a signal received from an isolation communication channel toobtain gate information and configuration information simultaneouslytransmitted over the isolation communication channel. The demodulatorincludes a plurality of demodulation paths. The signal includes a firststate in which the signal oscillates at a first frequency for a firstbit time, a second state wherein the signal oscillates at differentfrequencies during a second bit time, a third state in which the signaloscillates at a third frequency lower than the first frequency during atleast a portion of a third bit time, and a fourth state in which thesignal is steady state for a fourth bit time. An envelope detector inone of the demodulation paths detects the second state.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood, and its numerousobjects, features, and advantages made apparent to those skilled in theart by referencing the accompanying drawings.

FIG. 1 illustrates a prior art system with an isolated gate driver.

FIG. 2A illustrates a system with an isolated gate driver with twoisolation communication channels to transmit gate and configurationinformation.

FIG. 2B illustrates an embodiment of an isolated gate driver thattransmits two types of information across a single isolationcommunication channel.

FIG. 3 illustrates traditional on-off keying (OOK).

FIG. 4 illustrates an embodiment of a high level block diagram of atransmit side of an isolated gate driver.

FIG. 5 illustrates a serial word for transmission across an isolationcommunication channel that provide drive strength information.

FIG. 6 illustrates an embodiment of a configuration detect and mapcircuit.

FIG. 7 illustrates an embodiment of mapping configuration parameters todrive current strength.

FIG. 8 illustrates an embodiment of a modulation scheme that allowssending configuration information and gate information simultaneously.

FIG. 9 illustrates a high level diagram of a modified OOK modulator.

FIG. 10 illustrates a block diagram of an embodiment of a receivecircuit.

FIG. 11 illustrates additional aspects of an embodiment of thedemodulator portion of the receive circuit.

FIG. 12 illustrates waveforms showing operation of the demodulatorportion.

FIG. 13 illustrates the fast and slow paths of the configurationdemodulation according to an embodiment.

FIG. 14 illustrates additional details of an embodiment of the envelopedetector.

FIG. 15 illustrates processing of the serial out data from theconfiguration demodulator.

FIG. 16 illustrates a sampling circuit to sample the data from theconfiguration demodulator.

FIG. 17 illustrates a timing diagram of the sampling circuit.

FIG. 18 illustrates an embodiment showing how the drive strengthinformation is used to control the drive strength of transistorsgenerating the gate signal.

FIG. 19 illustrates an embodiment showing how the drive strengthinformation is used to generate a gate signal combined off-chip.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

A typical CMOS digital isolation solution has a single communicationchannel 109 as shown in FIG. 1 . A second isolation communicationchannel would normally be required to dynamically transmit informationother than gate information, such as status bits, configuration bits,etc., through the isolation barrier. The gate signal is a criticalcontrol function that cannot be delayed while configuration informationis being sent. Accordingly, referring to FIG. 2A, in order to provideconfiguration information in addition to the gate information, e.g.,dynamic drive strength information, the system 200 utilizes an isolatedgate driver 201 with a separate isolation communication channel 210 tosend the configuration information. Separate transmitter circuits 206Aand 206B transmit the gate and configuration information, respectively,to receiver circuits 208A and 208B on the secondary side utilizing thetwo isolation communication channels 209 and 210. The transmittercircuit 206A transmits the gate information over the first isolationcommunication channel 209. The transmitter circuit 206B transmits theconfiguration information (information other than gate information),over the second communication channel 210. The illustrated differentialisolation communication channels 209 and 210 each transmit a positive(TX-P) signal and a negative signal (TX-N). The illustrated isolationcommunication channels 209 and 210 utilize capacitive isolation althoughother embodiments may utilize various approaches to isolation such asinductive coupling or optical coupling to communicatively couple thetransmit circuits 206A and 206B and the receive circuits 208A and 208B.Thus, the physical implementation of the isolation communicationchannels may differ in different embodiments.

The secondary side includes driver circuitry (e.g., included in receivercircuit 208A), that generates gate signal 216 based on the GATE signalreceived from the primary side and provides the gate signal 216 to thegate of device 218. In an example embodiment, the high-power device 218controls power delivered to a load. Exemplary high-power devices includepower metal-oxide-semiconductor field-effect transistors (MOSFETs),insulated-gate bipolar transistors (IGBTs), Gallium-Nitride (GaN)MOSFETs, Silicon-Carbide (SiC) power MOSFETs, and other suitable devicesable to deliver high power signals.

In embodiments there are two aspects of the gate signal 216 that arecontrolled. The receive circuit 208A controls both whether the gatesignal is on or off and also controls the drive strength of the gatesignal 216 based on configuration information received from the receivecircuit 208B.

Thus, as explained above, in one approach the second isolationcommunication channel carries configuration information. While providinga communication path for configuration information is beneficial, thesecond communication channel 210 consumes additional power and requiresadditional silicon area. In addition, package limitations can oftenprevent the inclusion of a second isolation communication channel. Inorder to overcome package limitations and the disadvantages due toadditional power and area of a second isolation communication channel,while still providing dynamic configuration information, embodimentsdescribed herein send configuration information simultaneously with themain digital gate signal over a single isolation communication channelwithout affecting the main performance requirements of the main digitalsignal.

Referring to FIG. 2B, in an exemplary embodiment, the system 220includes an isolated gate driver 221 that includes a transmitter circuit226 and a receiver circuit 227 communicatively coupled across anisolation barrier through use of isolation communication channel 228.The system 220 includes a primary side integrated circuit (containingtransmitter 226) and a secondary side integrated circuit (containingreceiver 227) respectively disposed in first and second voltage domains.In embodiments, transmitter circuit 226 is formed on a first integratedcircuit die and receiver circuit 227 is formed on a second integratedcircuit die, both of which are attached to a lead frame and includeterminals coupled to isolation channel 228 formed on the lead frame andpackaged as a single device. In still other embodiments, transmittercircuit 226 and receiver circuit 227 include terminals coupled to theisolation communication channel 228, all of which are formed on anintegrated circuit die. In still other embodiments transmitter circuit226 and receiver circuit 227 are integrated circuits included in amulti-chip module. In embodiments, terminals of the transmitter circuitand receiver circuit are coupled to external elements, e.g.,transformers, discrete resistors, and discrete capacitors within themulti-chip module or to terminals of the package of the multi-chipmodule, and to a package of controller 222.

In embodiments the transmitter circuit 226 and receiver circuit 227utilize modified on-off keying (OOK) to allow the main digital signal tobe sent simultaneously with configuration information over the singleisolation communication channel 228. Compared with a two channelimplementation shown in FIG. 2A in which one channel is used for themain digital signal and the other channel is used for configurationinformation, embodiments described herein use a single isolationcommunication channel thereby consuming less power and utilizing lesssilicon die area. In an example, as described further herein, the singleisolation communication channel 228 carries both gate information forgate signal 230 to drive transistor 232 and drive strength informationfor the gate signal 230.

FIG. 3 illustrates traditional on-off keying (OOK) modulation. OOK is aform of amplitude-shift keying modulation that represents digital dataas the presence or absence of a high frequency signal on thecommunication channel. For example, when the GATE signal (e.g. to drivethe gate of transistor 232 in FIG. 2B) is a logic “0”, the transmittertransmits a steady state signal (OV) at 301 on the differentialisolation channel (TXP-TXN) where TXP is the positive transmitted signaland TXN is the negative transmitted signal for the differential pair.When the GATE signal is a “1”, the transmitter transmits a highfrequency signal at 303 over the isolation communication channel, e.g.,with a frequency of 500 MHz. Thus, the presence of the high frequencyrepresents a binary one, while its absence represents a binary zero.However, traditional OOK can only send one piece of data at a time. Incontrast, embodiments described herein transmit the main digital signal(e.g., the gate signal) along with configuration (or other) informationover the single isolation communication channel. The main digital signalcan be a logical one or a zero and at the same time the configurationinformation can also be a logical one or zero regardless of the logicalvalue of the main digital signal.

FIG. 4 illustrates a high level block diagram of an embodiment of thetransmit side 400 of an isolated gate driver. In the illustratedembodiment, gate information 401 from controller 222 (FIG. 2B) providesthe information used for the main digital signal—the gate signal. Inaddition, the transmit side receives configuration information on inputterminals 403 and 405. The configuration information may be provided invarious forms, such as an analog voltage, a current, a digital voltage,or through resistance values of resistors coupled to the input terminals403 and 405. The transmitter circuit transmits the configurationinformation simultaneously with the gate information over a singleisolation communication channel. The configuration detect and mapcircuit 407 receives the parameters (voltage, current, digital value,resistance) present on input terminals 403 and 405 and maps theparameters to a particular drive strength value. In an embodiment, theconfiguration detect and map logic is made aware of whether to mapvoltage values, current values, digital values, or resistance values tothe drive strength. That may be accomplished through a one-timeprogrammable memory (OTP) that is programmed with the type of parametersbeing supplied to the isolated gate driver. In an embodiment, theconfiguration detect and map logic maps the configuration information toa three bit value (P2, P1, P0) for configuration CONFIG. 1 and a threebit value (N2, N1, N0) for CONFG2. In an embodiment, P2, P1, P0 controlsthe drive strength of the gate signal generated by PFETs when the gatesignal is pulled up and N2, N1, NO controls the drive strength of thegate signal generated NFETs when the gate signal is pulled down. Theconfiguration detect and map circuit 307 supplies the three bit digitalvalues to the parallel to serial logic circuit 409 that converts theparallel bits to a serial word. In an embodiment, the parallel to seriallogic circuit 409 also adds a start bit, parity, and redundancy to theserial word, as shown in FIG. 5 , for transmission across the isolationcommunication channel. For example, bit (P2) and its complement (P2 )are transmitted over the isolation communication channel. Otherembodiments add additional parity bits to provide for multi-bit errorcorrection or for other error checking techniques. Each serial bit istransmitted on the isolation communication channel along with a value ofthe GATE signal. A typical serial bit time is 1 or 2 μs but otherembodiments use a bit time of a different length. Logic 409 supplies theserial word to the transmit OOK modulation circuit 411, which isdescribed further herein. The transmit OOK modulator also receives thegate signal from input terminal 401.

FIGS. 6 and 7 illustrate additional details of the configuration detectand mapping circuit 401. In an embodiment, the resistance values ofresistors 601 and 603 coupled to input terminals 403 and 405 determinethe drive current strength of the gate signals. The current from currentsources 607 and 608 cause voltages across resistor 601 and variableresistor 609, and comparator 610 receives the two voltages. Thesuccessive approximation register (SAR) 611 adjusts the variableresistor 609 until the comparator 610 indicates the voltages on itsinputs are equal, e.g., when the comparator output changes polarity,thereby indicating that the SAR setting corresponds to the value of theexternal resistor 601. Mapping logic 615 maps the final SAR value (orequivalent resistance value) to a three bit code indicating drivecurrent strength as explained in more detail in the example of FIG. 7 .The configuration information on input terminal 405 is similarlydetermined using current sources 617 and 619, variable resistor 621,comparator 623, and SAR 625. SAR 625 is adjusted until the voltages atthe inputs of comparator 623 are the same, thereby indicating the valueof external resistor 603.

In another embodiment a voltage level is supplied on input terminals 403and 405 to specify the configuration information rather than usingresistors 601 and 603. In such an embodiment, rather than connectingresistors, the controller 222 (see FIG. 2B) supplies a voltage to theinput terminals from, e.g., a digital to analog converter (DAC) in thecontroller. To operate in the “analog voltage” mode, the current source607 is turned off and current source 608 supplies a known current tovariable resistor 609. The SAR 611 adjusts the variable resistance untilthe comparator 610 indicates the voltages at its inputs are equal. Thevoltage across the variable resistor 609 is supplied to the mappinglogic or the SAR output (the variable resistance setting) is interpretedas an estimate of the voltage level seen at terminal 403. The detectionof the voltage on input terminal 405 is similarly accomplished. Thecurrent source 617 is turned off and current source 619 supplies a knowncurrent. SAR 625 adjusts the variable resistance 621 until thecomparator 623 indicates the voltages at its inputs are equal. Thevoltage across the variable resistor 621 (or the SAR output) is suppliedto the mapping logic 615, which interprets the SAR setting as anestimate of the voltage seen at terminal 405.

In still another mode of operation, rather than resistors or analogvoltages being applied to the input terminals receiving configurationinformation, a digital value is applied to the input terminals allowingthe selection of two different values for the configuration informationon each input terminal. In an embodiment of “digital” mode, the currentsource 607 is turned off and the current source 608 supplies a currentto a fixed resistance value of the variable resistor 609 that causes athreshold voltage value to be supplied to the comparator. That thresholdvoltage distinguishes a logic 1 from a logic 0. The comparator outputmay be supplied directly to the mapping logic 615. In other digitalembodiments, a separate comparator is used to determine a logic 0 or 1.In still other embodiments, one or more of terminals 403 and 405function as a serial input port and the configuration is supplied in adigital word allowing greater selection of configuration settings. Thecircuitry associated with input terminal 405 operates in digital mode ina similar manner to the operation of the circuits described withrelation in input terminal 403. Many other circuits can be used todetermine voltages, resistance, current, capacitance, or otherparameters values on terminal 403 and 405. The circuits shown in FIG. 6are examples and many other circuits can be used to receive anddetermine parameter values that would be apparent to those of skill inthe art.

FIG. 7 illustrates an embodiment of the mapping functionality, whichmaps resistance, analog voltage, or digital values to a particularconfiguration value. In an embodiment, the mode of operation (analogresistance, analog voltage, digital) is programmed into a one timeprogrammable memory 625, e.g., through a interface 627. In otherembodiments the mode of operation may be programmed into the other kindsof memory in the transmitter integrated circuit, e.g., non-volatilememory (NVM). With reference to the embodiment of FIG. 7 , in “analogresistance” mode 701, resistance values map to configuration statesS0-S7, represented by 3 bits. The three bits map to eight differentdrive current strengths shown as drive current strength percentages 705.FIG. 7 shows that the various configuration states S0-S7 map to aparticular percentage drive current strengths ranging from 8.75% to 100%of the maximum drive current. For example, a resistance near the valueof 4.42 kΩ (state S2) maps to a 17.5% drive current strength. Thus,17.5% of a maximum drive current strength is utilized to drive at leastone value of the gate signal. The particular percentages are onlyexamples and other embodiments may utilize different percentages ofdrive current strength and a different number of configuration bits.Note that the resistance values are illustrative and other resistancevalues may be used in other embodiments.

The table in FIG. 7 also shows how in “analog voltage” mode voltagelevels 703 on the input terminals map to the different configurationstates. For example, a voltage level near 221 mV (state S2) maps to adrive current strength percentage of 17.5%. In voltage mode, acontroller (e.g., controller 222 in FIG. 2B) supplies the voltage to theinput terminal. While an analog voltage mode is shown, other embodimentsuse an analog current and map analog current values to the configurationstates.

In “digital mode” an external controller, e.g., controller 222 (FIG. 2B)drives the configuration terminals with digital signals and states S0and S8 are mapped to arbitrary drive strength values shown asp/nfet_str_low and p/nfet_str_high. For example a digital “0” on pin 403maps to pfet_str_low and a digital “1” on pin 403 maps to pfet_str_high,and a digital “0” on pin 405 maps to nfet_str_low and a digital “1” onpin 405 maps to nfet_str_high. PFET and NFET transistors (see, e.g.,FIG. 18 ) are used to generate the gate drive signal. In an embodiment,the drive strength values for digital mode are programmed into OTP (orNVM). The particular mappings for resistance, voltage, and percentagesmay also be programmed into the memory (OTP, NVM, or other) used by themapping logic 615.

In an embodiment, the configuration terminals also provide a disablefeature to disable the transmitter. A bit in memory (OTP, NVM, or other)is set to indicate the disable feature is enabled. The disable featuredisables the transmit signal path in the transmit circuit if the stateS8 is received in either the analog (resistance or voltage) or digitalmode. The disable feature may cause 0V to be coupled to the transmitsignal path or otherwise disable transmissions. In analog voltage mode avoltage >850 mV maps to S8 and in analog resistance mode a highimpedance (hiZ) value maps to S8. In digital mode a logical 1 indicatesthe S8 state and thus disable mode. With the disable feature enabled,the digital mode only provides a single drive current strength value inS0. With this disable feature, a single pin can be used the control boththe drive strength and enable/disable function of the transmitter, thusallowing more features in a smaller pin count package.

In an embodiment, an additional bit(s) in memory (OTP, NVM, or other)indicates use of a single pin (rather than two) to indicate signalstrength. In an embodiment, the additional bit always indicates aparticular input terminal is to be used, e.g., if the single pin bit isset, always use input terminal 403. In other embodiments, additionalbits may be used in single pin mode to indicate which input terminal isthe “single pin.” Thus, in the single pin mode the drive strengthinformation from only one of the configuration pins is used to generateboth P2, P1, P0 and N2, N1, N0. With the single pin mapping to both Pand N functions, drive strength control can be utilized in reduced pincount packages where only a single pin is available for strength controlfunction. Embodiment may include capability to support any or all of theseveral modes of operation, including analog/digital, disable/notdisable, and single pin/not single pin.

Referring again to FIG. 6 , once mapping is complete, the parallel datais converted to serial in logic 409 and a start bit, redundancy (to theextent desired) and parity is added for serial transmission across theisolation communication. The serial data is supplied to the OOKmodulator 411, which modulates the serial configuration data and thegate signal. FIGS. 8 and 9 illustrates operation of the OOK modulator.

FIG. 8 illustrates an embodiment of the modulation scheme that allowssending both configuration information and gate informationsimultaneously. To transmit configuration information having a value ofCONFIG=0, with GATE=0, a constant voltage is sent as shown at 801. ForCONFIG=1 and GATE=0 the signal is modulated at a frequency of 64 MHz asshown at 802. For CONFIG=0 and GATE=1, as shown at 803, the signal isfrequency modulated at the OOK frequency. In an embodiment the OOKfrequency is 450 MHz. The OOK frequency should be high enough to readilydistinguish from the lower frequency signal when CONFIG=1 and GATE=0.Finally, for GATE=1 and CONFIG=1, the signal is frequency modulated attwo frequencies during the bit time with a first frequency shown at 805and a second frequency shown at 807. The frequencies are contained inenvelope 809. In an embodiment, the frequency shown at 807 is 450 MHzand the frequency shown in 805 is 550 MHz and the envelope 809 is an 8MHz envelope. Thus, the modulator is responsive to the GATE signal toprovide straight OOK modulation (a 0 or 450 MHz signal) with the CONFIGsignal at 0 and provides an adjustment to the OOK signal with the CONFIGsignal=1 (˜64 MHz or 450/550 MHz). Note that the frequency deviation ofthe transmitted signal is substantially larger in response to changes inthe GATE signal as compared to changes in the CONFIG signal. Forexample, changes in the GATE signal cause the modulation frequency tochange from 0 to 450 MHz. In contrast, changes in the CONFIG signal,assuming the GATE signal is constant, cause the modulation frequency tochange from 0 to 64 MHz or from 450 MHz to 550 MHz. This frequencyseparation helps ensure an accurate demodulation of the GATE signal.

FIG. 9 illustrates an embodiment of the OOK modulator 411. The modulatedsignal generated is based on the values of the CONFIG signal 901 and theGATE signal 903 to generate the signal shown in FIG. 8 that representsfour states (two binary values for CONFIG and two binary values forGATE). The AND gate 905 receives the CONFIG signal 901 and the envelopesignal 911. Oscillator control logic 908 receives the output of AND gate905 and controls whether oscillator 909 generates a 450 MHz signal or a550 MHz signal. An output of 0 from AND gate 905 causes the oscillator909 to generate a 450 MHz signal and an output of 1 causes theoscillator to generate a 550 MHz signal. The oscillator 909 may beimplemented as a ring oscillator with different taps for differentfrequencies or different supply voltages or currents, an LC oscillatorwith adjustable capacitance, or any other suitable oscillator. WithCONFIG=0, the oscillator 909 generates a 450 MHz signal and withCONFIG=1 the oscillator 909 generates the 450 MHz signal and the 550 MHzsignal at a rate determine by the frequency of the envelope signal 911.For example, with an 8 MHz envelope signal, the 450 MHz signal and the550 MHz signals repeat at an 8 MHz rate as shown in FIG. 8 . The dividercircuit 915 divides the oscillator output signal by 8 or otherappropriate divide value to readily distinguish the lower frequencysignal from the 450/550 MHz signal. With CONFIG=0, AND gate 917 suppliesa 0 to multiplexer 919. Multiplexer 919 receives an input signal fromthe oscillator 909 and another input signal from AND gate 917. The valueof the GATE signal selects the input provided on the output ofmultiplexer 919. With GATE=1, the multiplexer selects the oscillatoroutput signal (450 MHz or 450/550 MHz) as the multiplexer output signaldepending on the value of CONFIG. With GATE=0, the multiplexer selectsthe output of AND gate 917, corresponding to the signals shown 801 or802. AND gate 917 supplies either a 0, with CONFIG=0 or the output ofdivider 915 with CONFIG=1. Note that in the embodiment of FIG. 9 , withCONFIG=1, and GATE=0, the divider divides the oscillator output thatvaries according to the envelope signal. Thus, the divide by 8 signal is450/8 MHz and 550/8 MHz with the envelope signal 911 determining therate of change between the two frequencies. In other embodiments, theGATE signal is also supplied to control logic 908 and having GATE=0 andCONFIG=1 and the control logic 908 forces the oscillator output to befixed at either 450 MHz or 550 MHz in that state and thus the frequencyat 802 to be fixed at 56.25 MHz or 68.75 MHz. The 64 MHz signalrepresents a suitable frequency for that particular state with GATE=0and CONFIG=1 but the frequency can be higher, lower, or varyingaccording to the particular embodiment. The signal from multiplexer 919is then supplied to drivers 921 and 923 and transmitted over theisolation communication channel. The transmitted signal is then receivedby the receiver coupled to the isolation communication channel, and issent to a demodulator to recover the GATE signal and the CONFIG signal.The GATE signal controls the transistor coupled to the receiver circuitand the CONFIG information is de-serialized to recover the configurationbits, which are then used, e.g., to control the drive strength of theGATE signal.

The drive strength aspects of the modulator shown in FIG. 9 is easilydisabled, e.g., by setting CONFIG 901 to 0, and then the OOK signalreturns to a traditional OOK modulation with a 1 indicated by a 450 MHzsignal and a 0 indicated by a steady state voltage such as 0V. In thatway, in applications where no drive strength signal is provided, themodified OOK modulator can operate as a standard OOK modulator. In anembodiment, the configuration of this modified OOK modulator into astandard OOK modulator is implemented by OTP control in a similar way asdescribed in other aspects of embodiments described herein.

Another embodiment waits until GATE=1 to transmit configurationinformation. The OOK signal is frequency modulated to represent CONFIG=1(or 0) as shown at 805 and 807 and the OOK signal is a fixed frequencyas shown at 803 to represent a CONFIG=0 (or 1). That approach has thebenefits of being simpler but limits the transition to only when themain signal (e.g., GATE) is one. Also, instead of frequency modulation,other embodiments pulse width modulate the OOK signal when GATE=1, butthat approach becomes more difficult for high OOK frequencies in whichthe pulse with is small.

Various other modulation schemes can be used. For example, fourfrequencies can be used to represent the four states represented by GATEand CONFIG. In some of these embodiments, the GATE signal changingcauses a much larger frequency deviation at the output of the modulatorthan changes in the CONFIG signal. In this way, the integrity of theGATE signal could be maintained while only relatively small frequencychanges caused by the CONFIG signal would only cause minor changes tothe demodulation of the GATE signal. Alternatively, various patterns of1s and 0s may be used during a bit time to represent different values.

FIG. 10 illustrates a block diagram of portions of an embodiment of thereceiver 227 shown in FIG. 2B. The receiver receives a differentialsignal that was transmitted over the isolation communication channel andis received as the differential signals RXP and RXN. Those signals areamplified in one or more amplifiers 1001 and supplied to an OOKdemodulator 1003 to demodulate gate information from the receiveddifferential signal and supply the gate signal 1005. The gate signal andthe received signal, after amplification, are supplied to aconfiguration demodulation path 1007 that extracts the configurationinformation from the received differential signal and supplies theconfiguration information to the clock recovery, deserializer, and errorcheck circuit 1009. The clock recovery, deserializer, and error checkcircuit 1009 converts the serial data stream received over the isolationcommunication channel to a parallel word of configuration information,e.g., 3 bits, to apply as drive strength signals to the driver controllogic 1010. Thus, the clock recovery, deserializer, and error checkcircuit 1009 recovers a clock signal to sample the serial out data 1012from the configuration demodulation path 1007, recreates P2, P1, P0 andN2, N1, and N0, checks the parity bits, redundancy bits, or otherwiseperforms the error checking to ensure the data is correct beforeupdating the configuration setting of the driver control circuit 1010.If errors are found, the drive strength values are not updated. Otherconfiguration settings may also be controlled by the configurationinformation transmitted. For example, the configuration information canspecify the type of error reporting desired, default values for drivestrength, or turn on and off times for the high-power transistor. In theembodiment of FIG. 10 two output terminals 1020 and 1022 are used tosupply the turn on and turn off signals for the gate signal, which arecombined externally to drive the power transistor. The VOP pin 1020provides the positive drive current to turn on the power transistor andthe VON pin 1022 provides the sinking current to turn off the powertransistor. Other embodiments utilize a single output terminal for thegate signal. The strengths of the drive currents provided by the drivercontrol logic 1010 are controlled by the configuration information.

FIG. 11 illustrates additional details of an embodiment of thedemodulator in the receive circuit. The demodulator includes a gatedemodulation path 1101 and a configuration demodulation path 1102. FIG.12 illustrates example waveforms involved in the demodulation of thetransmitted signal. In the example waveforms of FIG. 12 ISORX 1104, thereceived signal after amplification, starts at a state representingCONFIG=1 and GATE=0 (oscillating at 64 MHz) and then changes to CONFIG=0and GATE=1 (oscillating at 450 MHz). With reference to FIGS. 11 and 12 ,the amplifier 1103 supplies an amplifier output ISORX 1104 to a filter1105. In an embodiment, filter 1105 is implemented as a bandpass filterwith a center frequency around 500 MHz, and a bandwidth such that it canpass 450 MHz and 550 MHz, but will reject other frequencies such as 64MHz, and those frequencies associated with noise in the system. Thefilter 1105 supplies a filter output 1106 as an input to a root meansquare (RMS) detect circuit 1107. The RMS detect circuit 1105 detectsthe energy in the received signal and supplies an RMS output signal1108, to comparator 1109 and comparator 1111. The comparator 1109compares the RMS detect output 1108 to a reference voltage REF1 shown inFIG. 12 . In FIG. 12 , the RMS output 1108 is below REF1 (when ISORXoscillates at 64 MHz) until 1201 at which time the RMS output signal1108 goes above the voltage threshold REF1 indicating the RMS valuecorresponds to an oscillation value of at least 450 MHz. At that timethe GATE signal 1110 goes from 0 to 1. Note that if the oscillation was450/550 MHz (GATE=1, CONFIG=1), the GATE signal supplied by comparator1109 would still be a 1 as the RMS detect output 1108 would still beabove REF1. Thus, gate demodulation path 1101 functions as an OOKdemodulator and looks for oscillations at or above a certain frequency(450 Mhz) and ignores oscillations below that frequency, thus ignoringthe modifications to the OOK signal caused by CONFIG=1, when GATE=0,resulting in ISORX oscillating at approximately 64 MHz. When the RMSdetect output rise above REF1, the GATE signal 1110 from the comparator1109 goes to one and when the RMS detect output falls below REF1, thegate signal 1110 goes to 0.

In one part of the configuration demodulation path, comparator 1111compares the output 1108 of the RMS detect circuit 1107 to the voltagethreshold REF0. As shown in FIG. 12 the compare results in anoscillating signal 1115 at 128 MHz when ISORX is oscillating at 64 MHz(GATE=0 and CONFIG=1). When ISORX is 0, the slow path signal is zero andwhen ISORX is 450 MHz or 450/550 MHz, the slow path signal 1115 is a“1”. The comparator 1111 supplies the slow path signal 1115 to thedigital demodulation block 1118, which includes sub-demodulation pathsdescribed further herein.

The fast path signal 1117 of the configuration demodulation path comesfrom the output 1104 of the amplifier 1103 and the fast path signal issupplied (with the 8 MHz envelope present when GATE=1 and CONFIG=1 andwithout the envelope present when GATE=1 and CONFIG=0) to the digitaldemodulation block 1118. Schmitt trigger 1120 converts the output of theamplifier 1103 (after a buffer circuit) to a digital value for thedigital demodulation block 1118. Note that some circuits in the gatedemodulation path and the configuration demodulation path are shared.

FIG. 13 illustrates additional details of sub-demodulation paths 1301(slow path) and 1303 (fast path) of the configuration demodulation pathand some common elements in the configuration demodulation pathincluding the selector circuit 1305 and the counter 1307. Selectorcircuit 1305 selects the fast path signal or the slow path signalaccording to the value of the GATE signal 1110. If the GATE signal is“1”, implying the transmitted signal is at least 450 MHz, the selectorcircuit 1305 selects the fast path signal 1117. If the GATE signal is“0”, implying the transmitted signal is ˜64 MHz (varying between 56.25MHz and 68.75 MHz in the embodiment illustrated in FIG. 9 ), or lower infrequency, the selector circuit selects the slow path signal 1115. Theripple counter 1307 counts the number of pulses from the fast pathsignal or slow path signal and supplies the count value to the fast pathsub-demodulation path 1303 and to the slow path sub-demodulation path.The counter 1307 is periodically reset by reset signal 1306. The slowpath sub-demodulation path 1301 receives the count value 1308 andcompares the count value to integer values to see if the count value iswithin a frequency range bounded by the integer values M and N. If thecount value is above a minimum value M and below a maximum value N, thenthe frequency of the slow path signal is within the frequency range(e.g., a frequency range including 128 MHz) and the output 1312 from ANDgate 1310 goes to a “1”. If count value is below M, e.g., CONFIG=0 thenAND gate 1310 supplies a “0” on output 1312. If the count value is aboveN, indicating the slow path signal has a higher frequency than, e.g.,˜128 MHz, then AND gate 1310 supplies a “0”.

The fast path sub-demodulation path 1303 receives the count value atcompare logic 1314 and selector circuit 1316. The compare logic 1314determines if the count value is greater than or equal to an integer P,thereby indicating the frequency of the transmitted signal (and the fastpath signal) is above a predetermined frequency, e.g. 450 MHz. If thecounter value 1308 is less than P, the selector circuit 1316 selects 0and otherwise selects the count value. The envelope detector 1318detects the presence of an envelope, e.g., the 8 MHz envelope shown inFIG. 8 . In an embodiment the envelope detector 1318 implements a singlefrequency of a discrete Fourier transform (DFT) to find the energy at 8MHz and detect the envelope. Thus, if the count value is changingbetween periodic resets based on a 450 MHz/550 MHz transmitted signal(GATE=1, CONFIG=1), the envelope is detected and the output of theenvelope detector goes to “1”. If on the other hand, no envelope isdetected, e.g., the transmitted signal is 450 MHz 1(GATE=1, CONFIG=0)the output of the envelope detector is “0”. The output 1320 of theenvelope detector is combined in OR gate 1322 with the output 1312 ofAND gate 1310. A filter, e.g., a finite impulse response (FIR) filter1323 removes glitches from the output of OR gate 1320 and supplies aserial output 1324. Additional filters, e.g., additional FIR filters,may be used in the fast sub-demodulation path and slow sub-demodulationpath that are not shown for ease of illustration. The compare logiccompares the count value from counter 1307 to M, N, and P in anembodiment using 4 samples per 8 MHz envelope (using a 32 MHz internalclock signal) in the fast path and a similar number of counts areobtained for the 128 MHz input to the slow path. In an embodiment, thecomparison is made only for the selected path (active path) with thenon-selected path output to OR gate 1322 being forced to zero. The ideais that only one of the slow and fast paths is active at any point intime.

FIG. 14 illustrates additional details of the envelope detector 1318.The DFT 1402 supplies a filter 1404. The filter output is squared in1406 and comparator 1408 compares the bin energy from 1406 to areference value corresponding to the bin energy that would be present ifthe envelope were present at a minimum amplitude value. If the binenergy is greater than the reference, the envelope detector supplies a“1” and if the bin energy is not greater than the reference, theenvelope detector supplies a “0”.

Referring to FIG. 15 , the serial output 1324 from the configurationdemodulator is supplied to the clock recovery, deserializer, and errorcheck circuit 1009 (see FIG. 10 ) that samples the serial output insample circuit 1502, recreates the configuration information includingthe start bit, P2, P1, P0, N2, N1, NO, and parity bits and any otherredundancy bits in serial to parallel block 1504. Once the transmittedword is recovered, the error check logic 1506 checks for errors, e.g.,parity errors. If no errors are detected, the START bit, redundant bits,and parity bit(s) are removed and the recovered CONFIG values update thedriver strength (or other configuration settings) in the drive controlblock.

FIG. 16 illustrates an embodiment of sample logic 1502. The sample clocksignal is recovered from transitions of serial out and delayed to causethe sampling to occur in the middle of a serial out bit. A transitiondetector (1 to 0 or 0 to 1) can be used to generate a sampling pulsefrom sequential bits having a transition. The lack of transitions insequential bits, e.g., sequential 1s or 0s, requires another way todetermine a sample time. The delay block 1601 delays the serial outputand XOR gate 1603 compares the delayed serial output to the currentserial output. If the bits are different, indicating at transition, thecounter 1605 resets. Flip-flop 1607 receives the current serial out biton its D input. The pulse logic 1609 pulses the clock of flip-flop 1607when the counter equals 2. That places the pulse two clock cycles ofcounter 1605 after the transition. The counter's clock 1611 has a periodsuch that two cycles of the counter will place the sample pulse near themiddle of the serial out bit. If no transition is detected, the pulselogic 1609 also pulses when the count=5 to place the next pulse near themiddle of the next serial out bit. In an embodiment, the serial word isframed as shown in FIG. 5 , thus guaranteeing that at most twosequential bits are the same before a transition occurs. The counter isreset at the next transition. The output of the flip-flop 1607 issupplied to the error detection logic 1506.

FIG. 17 illustrates a timing diagram of the sample circuit 1502. Whenthe serial data out from filter 1323 (see FIG. 13 ) has an outputsequence “1”, “0”, “1”, the transitions (edges) at 1701 and 1703 drivethe pulses 1702 and 1704 (on count=2 after the edge). However, when twosequential “1s” (or “0s”) occur, the edge 1705 drives the first pulse1706 and count=5 drives the second pulse 1708. Due to the framing of theserial word an edge generated pulse should occur next after the countgenerated pulse 1708. Once the transmitted signal is successfullyreceived, the GATE information and CONFIG information is used by thedriver control block.

FIG. 18 illustrates how driver control block 1800 uses the drivestrength signals. PFET control logic 1802 receives the configurationbits Drive Strength P (P2, P1, P0) and adjusts the current supplied byPFET(s) 1804, where PFET 1804 is, e.g., 8 PFET transistors configured inparallel of the same or different sizes (width/length (W/L) ratios),that are used to adjust the current to achieve the percentage drivestrength shown, e.g., in FIG. 7 , and corresponding to the states S0 toS7 depending upon the setting. The PFET control logic 1802 includes (oris coupled to NVM or other memory) that specifies the drive strengthpercentages corresponding the configuration bits, and whether arbitrarydrive strengths have been provided, and if so, their drive strengthvalues (for S0 and S8) for operation in digital mode and other necessaryconfiguration information. The M configuration bits for the PFETs drivestrength, e.g., 3 bits, map to the N signal lines, e.g., 8 signal lines,to control the drive strength current on output terminal 1806, which iscoupled to the gate of power transistor 1808. Similarly, the NFETcontrol block 1810 receives M configuration bits (Drive Strength N) tocontrol the drive strength supplied by NFET(s) transistor(s) 1812. Thecontrol block 1810 maps the M configuration bits to N control lines toadjust the current supplied by NFET(s) 1812, where NFET 1812 is formedby, e.g., 8 NFET transistors in parallel of the same or different sizes,that are used to achieve the percentage drive strength shown, e.g., inFIG. 7 corresponding to S0 to S8. The PFET transistors 1802 and NFETtransistors 1812 also receive at their respective gates a complementaryversion of the GATE signal (assuming GATE is active high).

In an embodiment shown in FIG. 19 , rather than supplying a singleoutput 1806, the driver control block 1900, corresponding to drivercontrol block 1010 in FIG. 10 , separate output terminals 1902 and 1904(see VOP and VON in FIG. 11 ) are supplied by the PFETs 1804 and NFETs1812 and the output terminals are combined externally to drive a gate ofan external transistor 1906. The terminal 1902 provides positive drivecurrent to turn on the external transistor, e.g., IGBT 1906, while theterminal 1904 provides sinking current to turn off the externaltransistor 1906. While not shown, a Miller clamp may be used inconjunction with the two terminals.

Thus, a system with an isolation communication channel has beendescribed that simultaneously communicates gate and configurationinformation across the isolation communication channel. A modulator inthe transmitter encodes the information for dual communication and ademodulator decodes the transmitted information to achieve, e.g.,dynamic variable drive strength control of an isolated gate driver. Thedescription of the invention set forth herein is illustrative, and isnot intended to limit the scope of the invention as set forth in thefollowing claims. Other variations and modifications of the embodimentsdisclosed herein, may be made based on the description set forth herein,without departing from the scope of the invention as set forth in thefollowing claims.

What is claimed is:
 1. A method comprising: receiving a signaltransmitted across a single isolation communication channel as areceived signal; and demodulating the received signal to determinerespective values for gate information and configuration informationcontained in the received signal based on which of four states thereceived signal represents.
 2. The method as recited in claim 1, furthercomprising: demodulating the received signal in a gate demodulation pathto determine the gate information; and demodulating the signal in aconfiguration demodulation path to determine the configurationinformation.
 3. The method as recited in claim 2, further comprising:demodulating the received signal as an on off keying (OOK) signal in thegate demodulation path; and demodulating the received signal as amodified OOK signal in the configuration demodulation path.
 4. Themethod as recited in claim 3, wherein an output of the configurationdemodulation path is determined, at least in part, by an output of thegate demodulation path.
 5. The method as recited in claim 3 wherein theconfiguration demodulation path includes a first sub-demodulation pathand a second sub-demodulation path.
 6. The method as recited as claim 5wherein the configuration demodulation path includes an OOK demodulatorin the first sub-demodulation path and include an FM demodulator in asecond sub-demodulator path.
 7. The method as recited in claim 2,further comprising: demodulating the received signal in a firstsub-demodulation path of the configuration demodulation path to detectan envelope to determine the configuration information, presence of theenvelope indicating one of the four states and indicating the receivedsignal is changing between a first frequency and a second frequency at athird frequency.
 8. The method as recited in claim 7, furthercomprising: demodulating the received signal in a secondsub-demodulation path of the configuration demodulation path todetermine a frequency associated with the received signal anddetermining the received signal to be in another of the four statesbased on the frequency.
 9. The method as recited in claim 2, furthercomprising: demodulating the received signal in the configurationdemodulation path to detect the configuration information using a valueof the gate information determined in demodulating the received signalin the gate demodulation path.
 10. The method as recited in claim 9,further comprising: selecting a fast path signal or a slow path signalas a selected signal according to the value of the gate information; andsupplying the selected signal to a first sub-demodulation path and to asecond sub-demodulation path of the configuration demodulation path, thefast path signal having a higher frequency than the slow path signalwhen the fast path signal is selected as the selected signal, the fastpath signal and the slow path signal being based on the received signal.11. The method as recited in claim 2, further comprising: generating afirst demodulated signal in a first sub-demodulator of the configurationdemodulation path based on a detected frequency of the received signal;generating a second demodulated signal in a second sub-demodulator ofthe configuration demodulation path based on detecting presence orabsence of an envelope in the received signal; and generating aconfiguration demodulation path output based on one or both of the firstdemodulated signal and the second demodulated signal.
 12. The method asrecited in claim 2, further comprising: generating a parallel word ofconfiguration information based on sequential outputs of theconfiguration demodulation path; and updating a configuration of acircuit based on the configuration information.
 13. The method asrecited in claim 12, further comprising the step of checking theparallel word for errors, and not updating the configuration of thecircuit if an error are found.
 14. The method as recited in claim 1,further comprising: generating a gate signal to control a gate of afirst transistor using the gate information; and controlling acharacteristic of the gate signal using the configuration information.15. An apparatus comprising: one or more input terminals to receive asignal transmitted across an isolation communication channel; and ademodulator circuit coupled to the one or more input terminals todemodulate a received signal to obtain gate information and to obtainconfiguration information, respective values of the gate information andthe configuration information being determined according to which one offour states the demodulator circuit detects in the received signal. 16.The apparatus as recited in claim 15, wherein the demodulator circuitfurther comprises: a gate demodulation path to detect if the receivedsignal is oscillating above a predetermined frequency and supply a gatesignal indicative thereof; and a configuration demodulation path todemodulate the received signal to obtain the configuration information.17. The apparatus as recited in claim 16, wherein an output of theconfiguration demodulation path is determined, at least in part, by thegate signal.
 18. The apparatus as recited in claim 16, wherein theconfiguration demodulation path further comprises: a firstsub-demodulation path of the configuration demodulation path includingan envelope detector to detect if an envelope is present in the receivedsignal and supply a first sub-demodulation path output signal as anindication thereof, presence of the envelope indicating the receivedsignal is changing between a first frequency and a second frequency,presence of the envelope indicating one of the four states of thereceived signal and supply a fast path demodulation output signal; asecond sub-demodulation path of the configuration demodulation pathincluding a frequency detector to determine if the received signal iswithin a frequency range and supply a second sub-demodulation pathoutput signal as an indication thereof, being within the frequency rangeindicative of another of the four states and supply a slow pathdemodulation output signal; and wherein a configuration demodulatoroutput signal is determined based on one or both of the firstsub-demodulation path output signal and the second sub-demodulation pathoutput signal.
 19. The apparatus as recited in claim 16, furthercomprising: a serial to parallel conversion circuit coupled to theconfiguration demodulation path to generate a serial configuration wordbased on received signals during a plurality of bit times; and whereinthe serial configuration word is used to update one or moreconfiguration settings.
 20. The apparatus as recited in claim 19,further comprising: an error detection circuit to detect errors in theserial configuration word and not update the one or more configurationsettings if an error is detected in the serial configuration word. 21.An integrated circuit comprising: a demodulator to demodulate a signalreceived from an isolation communication channel to obtain gateinformation and configuration information transmitted oversimultaneously over the isolation communication channel, the demodulatorincluding a plurality of demodulation paths; wherein the signal includesa first state in which the signal oscillates at a first frequency forfirst bit time, a second state wherein the signal oscillates atdifferent frequencies during a second bit time, a third state in whichthe signal oscillates at a third frequency lower than the firstfrequency during at least a portion of a third bit time, and a fourthstate in which the signal is steady state for a fourth bit time; and anenvelope detector in one of the demodulation paths to detect the secondstate.